Let's consider the state transitions for PCM devices during capture.
The state diagram for a PCM device during capture is shown below.State diagram for PCM devices during capture.
The transition between SND_PCM_STATUS_* states is the result of executing an API call, or the result of conditions that occur in the hardware:
|NOTREADY||READY||Calling snd_pcm_channel_params() or snd_pcm_plugin_params()|
|READY||PREPARED||Calling snd_pcm_capture_prepare(), snd_pcm_channel_prepare(), or snd_pcm_plugin_prepare()|
|PREPARED||RUNNING||Calling snd_pcm_read() or snd_pcm_plugin_read(), or calling select() against the capture file descriptors|
|RUNNING||PAUSED||Calling snd_pcm_capture_pause() or snd_pcm_channel_pause()|
|PAUSED||RUNNING||Calling snd_pcm_capture_resume() or snd_pcm_channel_resume()|
|RUNNING||OVERRUN||The hardware buffer became full during capture; snd_pcm_read() and snd_pcm_plugin_read() fail|
|RUNNING||UNSECURE||The application marked the stream as protected, the hardware level supports a secure transport (e.g., HDCP for HDMI), and authentication was lost|
|RUNNING||CHANGE||The stream changed|
|RUNNING||ERROR||A hardware error occurred|
|OVERRUN, UNSECURE, CHANGE, or ERROR||PREPARED||Calling snd_pcm_capture_prepare(), snd_pcm_channel_prepare(), or snd_pcm_plugin_prepare()|
|RUNNING||PREEMPTED||Audio is blocked because another libasound session has initiated playback, and the audio driver has determined that that session has higher priority|
For more details on these transitions, see the description of each function in the Audio Library chapter.
Last modified: 2013-10-30